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feat: Branch Key Storage Changes for Mutations
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changes/2025-01-17_key-store-storage-mutations/background.md
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| [//]: # "Copyright Amazon.com Inc. or its affiliates. All Rights Reserved." | ||
| [//]: # "SPDX-License-Identifier: CC-BY-SA-4.0" | ||
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| # Branch Key Storage Changes for Mutating Branch Keys | ||
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| # Definitions | ||
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| ## All items of a Branch Key | ||
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| "All items of a Branch Key" is all the items | ||
| persisted in the Key Store with the same Branch Key ID; | ||
| these will be one or more DECRYPT_ONLY versions, | ||
| the ACTIVE version, and the Beacon Key. | ||
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| In this document, | ||
| the result of the kms:GenerateDataKeyWithoutPlaintext of a Branch Key Version | ||
| is the "Branch Key Version's Cryptographic Material". | ||
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| All the results of the kms:GenerateDataKeyWithoutPlaintext | ||
| of all items of a Branch Key | ||
| are the "Branch Key's Cryptographic Materials". | ||
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| ## MPL Consumer | ||
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| An "MPL Consumer" is a library, service, or other application | ||
| that uses the AWS Cryptographic Material Providers Library (MPL) | ||
| to manage cryptographic materials. | ||
| An "MPL Consumer" may or may not be using an AWS Crypto Tools product, | ||
| such as the AWS Encryption SDK or the AWS Database Encryption SDK. | ||
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| ## Conventions used in this document | ||
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| The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", | ||
| "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be | ||
| interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119). | ||
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| # Background | ||
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| The [branch key store](../../framework/branch-key-store.md) | ||
| persists Branch Keys and their metadata; | ||
| the [Key Storage Interface](../../framework/key-store/key-storage.md) | ||
| is the interface for persisting this data. | ||
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| The Interface does yet specify how to safely change | ||
| properties of these Branch Key items. | ||
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| This change adds new Operations to the interface, | ||
| which facilitate changing the | ||
| properties of all items of a Branch Key. | ||
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| These new operations are constructed with _Optimistic Locks_, | ||
| ensuring that modifications do not accidentally erase data. | ||
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| Additionally, | ||
| they facilitate the creation, maintenance, and deletion | ||
| of items that are used to ensure a change to a Branch Key | ||
| is consistently applied to all items of that Branch Key. | ||
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| # Design Questions | ||
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| These are not answered, | ||
| as the Mutations Background document addresses | ||
| these questions. | ||
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| # Changes | ||
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| ## New Structures | ||
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| The following structures are introduced to the Key Storage Interface: | ||
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| ### EncryptedHierarchicalKeys | ||
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| A List of | ||
| [EncryptedHierarchicalKey](../../framework/key-store/key-storage.md#encryptedhierarchicalkey). | ||
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| ### MutationCommitment | ||
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| A structure holding information on | ||
| an in-flight Mutation of a Branch Key | ||
| that is never updated in-flight. | ||
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| The members are: | ||
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| - `Identifier`: a string, The Branch Key (ID) under Mutation | ||
| - `CreateTime`: a string, The ISO 8061 UTC Timestamp of when the Mutation was started | ||
| - `UUID`: a string, A unique identifier for the Mutation | ||
| - `Original`: a binary blob, A commitment of the original mutable properties of the Branch Key | ||
| - `Terminal`: a binary blob, A commitment of the terminal mutable properties of the Branch Key | ||
| - `Input`: a binary blob, A Description of the input to initialize a Mutation | ||
| - `CiphertextBlob`: a binary blob, which MAY be used to protect the Mutation Commitment | ||
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| ### MutationIndex | ||
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| A structure holding information on | ||
| an in-flight Mutation of a Branch Key | ||
| that is regularly changed in-flight. | ||
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| The members are: | ||
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| - `Identifier`: a string, The Branch Key (ID) under Mutation | ||
| - `CreateTime`: a string, The ISO 8061 UTC Timestamp of when the Mutation was started | ||
| - `UUID`: a string, A unique identifier for the Mutation | ||
| - `PageIndex`: a binary blob, Indirectly describes which items of the Branch Key have already been Mutated | ||
| - `CiphertextBlob`: a binary blob, which MAY be used to protect the Mutation Index | ||
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| ### OverWriteMutationIndex | ||
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| A structure, much like | ||
| [OverWriteEncryptedHierarchicalKey](../../framework/key-store/key-storage.md#overwriteencryptedhierarchicalkey), | ||
| that affords a conditioned update to the Mutation Index. | ||
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| The members are: | ||
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| - `Index`: The new Mutation Index | ||
| - `Old`: The last read Mutation Index | ||
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| ## New Operations | ||
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| The following new Operations are added: | ||
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| ### GetItemsForInitializeMutation | ||
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| Retrieves the items necessary to initialize a Mutation, | ||
| while checking for any in-flight Mutations. | ||
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| ### WriteInitializeMutation | ||
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| Atomically updates the Active Items | ||
| of a Branch Key along with | ||
| the Mutation Commitment and Mutation Index. | ||
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| ### WriteAtomicMutation | ||
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| Atomically updates all the Items of a Branch Key. | ||
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| #### QueryForVersions | ||
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| Query Storage for a page of version (decrypt only) items of a Branch Key. | ||
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| ### WriteMutatedVersions | ||
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| Atomically updates a page of version (decrypt only) | ||
| items while maintaining the Mutation Commitment and Mutation Index. | ||
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| ### GetMutation | ||
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| Check for Mutation Commitment on a Branch Key ID. | ||
| If one exists, returns the Mutation Commitment. | ||
| Otherwise, returns nothing. | ||
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| ### DeleteMutation | ||
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| Deletes an existing Mutation Commitment & Index. | ||
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| #### WriteMutationIndex | ||
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| Creates a Mutation Index, conditioned on the Mutation Commitment. |
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